Grasshopper , I work for a main dealer ( not subaru ) and for any dealer operating
in europe , they must operate under the "block exemption" ruling. This means that
a dealer cannot dictate where a car is serviced.
If you have to make a warranty claim and the dealer can put the failure down to the
car not being serviced correctly , then obviously they will void the warranty on that part.
Ensure the garage uses genuine parts and you shouldnt have a problem.
If you consult your dealer , ask for the service manager and mention "block exemption"
which was imposed by the european directive and he will probably cack his pants and
let you get the scoob serviced elsewhere and still honour your warranty.
Hope this is the info youre looking for.